The present invention relates to a poly-V pulley made of metal sheet used together with a V-belt for transmitting a rotational power and a method of manufacturing the same.
As a poly-V pulley of this kind, for the usage purpose of insertion and coupling onto a shaft via a one-way clutch or a bearing, known is a poly-V pulley of a structure in which a cylindrical peripheral wall is formed, an ear for preventing a V belt from disengaging is outwardly and protrusively formed in each of the axial ends of the outer peripheral face of the peripheral wall, and poly-V grooves are formed between both ears.
Generally, such a poly-V pulley is made of cast iron. However, the poly-V pulley made of cast iron is heavy. Moreover, the poly-V grooves are formed by cutting operations, thereby causing a problem of scattering many cut powders in workshops and worsening working environment. On the other hand, the poly-V pulley made of metal sheet, which is made of a flat plate material such as a rolled steel, has advantages: it is more durable, more lightweight and cheaper than the poly-V pulley made of cast iron.
The poly-V pulley made of metal sheet is disclosed in a gazette of Japanese Patent Laying-Open No. 8-300082. The disclosed poly-V pulley has steps wherein, preparatory to forming ears for preventing a V belt (called a belt guide in the gazette) from disengaging, on both axial ends of a peripheral wall portion, preliminary ears (called a portion in the gazette where a guide is formed) are formed on both ends of the cylindrical peripheral wall by means of a press process and a splitting process, and each preliminary ear whose structure is a single layer having a predetermined shape is subsequently shaped in the following step.
However, the ear having a single layer is thin so that the mechanical strength thereof is inferior. In order to obtain an ear having enough rigidity and an enough protrusive length, a thick blank is required. However, it is not easy to draw a thick blank so as to become a cup-shape with a bottom surface.
Then, an object of the present invention is to provide a poly-V pulley made of metal sheet having a superior rigidity, which makes it possible to obtain easily thick ears from the flat plate material whose thickness is not so great and which is easily drawn, and to ensure the length of the axial straight line of a bore of the cylindrical peripheral wall suitable for forcedly inserting the one-way clutch and the bearing, and a method of manufacturing the same.
A poly-V pulley made of metal sheet according to the present invention comprises:
poly-V grooves disposed between both ears on the outer surface of the peripheral wall,
wherein at least one of both ears includes an inner ear portion protruded from the end of the peripheral wall to the outward direction, and an outer ear portion folded back from the protruded outer end of the inner ear portion to an outer surface of the inner ear portion, so as to be closely fitted therewith, and the inner end surface of the ear is formed to be flush with the inner surface of the peripheral wall.
According to the poly-V pulley made of metal sheet, the inner and outer ear portions are folded to overlap with each other, thereby ensuring enough thickness of the ears so as to increase the rigidity, and making it possible to increase the length of the axial straight line of a bore of the peripheral wall only for a thickness of the outer ear portion. This is enough to ensure an effective contact supporting surface with the outer surface of the one-way clutch or the bearing which are forcedly fit into the inner surface of the peripheral wall.
In case that each ear on both ends thereof has a sectional structure wherein the inner and outer ear portions are folded so as to overlap each other, its rigidity is more enhanced than that of a case where only one ear has such a sectional structure. Therefore, the inner surface of the peripheral wall is finished by machining so as to have a predetermined inside diameter measurement and become completely circular, thereby making it possible to achieve an accurate finish so as to be suitable or forcedly fitting a one-way clutch, a bearing or the like.
A method of manufacturing a poly-V pulley made of metal sheet having the above structure, according to the present invention, comprises the steps of:
forming a cup-shaped forming body which has a bulging middle portion-peripheral wall like a barrel, integrated with an outer periphery of a circular bottom wall;
preparing a roller for forming ears provided with a concave forming surface and an annular projection, the concave forming surface which is concavely arc-shaped being disposed on an axial center portion of the outer surface, and the annular projection whose section is V-shaped being disposed on axially both ends of the concave forming surface;
applying a compressive load to the cup-shaped forming body in the axial direction at the same time while pressing the annular projection of the roller for forming ears against the outer surface of the bulging middle portion-peripheral wall in a radially inward direction thereof,
folding at least axial one end of the bulging middle portion-peripheral wall into two, and
protrusively forming inner and outer ear portions overlapped so as to be closely fitted with each other;
pressing a straightening roller having a shaping surface perpendicular to the outer periphery of the bulging middle portion-peripheral wall, against the outer surface of the bulging middle portion-peripheral wall in the radially inward direction thereof,
straightening the bulging middle portion-peripheral wall so as to be parallel with the axial direction, and
forming the perpendicular peripheral wall;
shaping the each poly-V groove between the ears on the outer surface of the perpendicular peripheral wall by means of rolling;
shearing a connecting portion between the bottom wall of the perpendicular peripheral wall and the ear, so as to remove the bottom wall; and
finally performing a machining work so as to make the inner end surface of the ear flush with the inner surface of the perpendicular peripheral wall.
According to such a manufacturing method, the compressive load is axially applied to the bulging middle portion-peripheral wall of the cup-shaped forming body, while the annular projections of the roller for forming ears are radially pressed against it. This can facilitate folding at least one end of the bulging middle portion-peripheral wall so as to closely fit the inner ear portion with the outer ear portion and be overlapped.